In pregnancies with human platelet
antigen (HPA)-1a incompatibility, data from retrospective
studies suggest that fetal/neonatal platelet counts are
lower in the second affected pregnancy. However, the only
prospective study of neonatal platelet counts
in 29 subsequent untreated pregnancies did not confirm this
finding [4].
When the index pregnancy was complicated by neonatal
alloimmune thrombocytopenia (NAIT), neonatal platelet counts
in the subsequent pregnancy were the same or higher in
two-thirds of cases. When the index pregnancy was
complicated by NAIT with severe thrombocytopenia, neonatal
platelet counts in the subsequent pregnancy were the same or
higher in 29 percent of cases. These findings, if confirmed
in larger studies, suggest that the severity of NAIT does
not consistently worsen in subsequent pregnancies. (See "Neonatal
alloimmune thrombocytopenia: Parental evaluation and
pregnancy management", section on 'Background'.)